Can Diamond Be Broken by Hydraulic Press?

Diamonds are an incredibly hard mineral, often used in engagement and wedding rings due to their strength.

However, diamonds are not indestructible. A strong impact such as a hammer can easily break them.

Hardness

Hardness is a measure of an object's resistance to scratching or denting. It depends on how atoms are arranged within crystal structure and the strength of chemical bonds between them.

Diamonds are considered to be the hardest minerals on Earth. They rank an astounding 10 on the Mohs scale, developed in 1812 by mineralogist Friedrich Mohs to measure scratch resistance of minerals.

It is essential to be aware that while diamonds may be the hardest material, they are not indestructible. A hydraulic press can easily crush a diamond.

The hardness of a material is determined by both its chemical bonds and crystallographic structure, consisting of interconnected layers of carbon atoms. Crushing diamonds is difficult but possible through hammering or cleaving along their cleavage lines.

The Vickers test is the most commonly used to gauge hardness. This tests how well a material resists plastic deformation when compressed with an indenter. Diamonds are 50% harder than cubic boron nitride (B2N), the second hardest mineral.

Tensile strength

Diamond is the hardest naturally occurring material, due to its strong covalent bonding. Unfortunately, diamond's toughness ranges from fair to good due to various structural weaknesses.

However, its theoretical intrinsic strength has been estimated to range from 90 GPa to 225 GPa depending on crystal orientation. Bulk diamond has been observed with compressive strengths up to 60 GPa and maximum tensile elastic strains exceeding 9%, suggesting its uniaxial tensile strength exceeds E/910 (where E is the Young's modulus10).

Theoretical tensile strength can be difficult to calculate directly. However, it can be determined through a combination of experimental and theoretical data. For instance, yield stress for strong single crystals can be estimated from the Hugoniot elastic limit and second- and third-order elastic constants12,13,14. Furthermore, dynamic yield stresses for germanium and silicon can be calculated using Knoop hardness tests15,16 as well as directly measured static values17,18,19.

Fracture toughness

One of the primary tensile properties of diamond is its fracture toughness. This property depends on both the orientation of a crack with respect to the forging axis and its size.

Vickers indentation tests are performed to assess diamond fracture toughness. A Vickers indent is made using either a diamond crystal or chemically vapor deposited (CVD) film, and then measured for length of radial cracks emanating from this indentation.

The critical value of the Mode-I stress intensity factor is used to measure fracture toughness. This test can be conducted on a single specimen, but it must be large enough for plane strain conditions at the crack tip.

At $mathcal M_hat kapprox 1.0times 10-3$, the fracture transforms from a radial, viscosity-dominated regime to one with buoyant toughness and an elongated inverse cudgel shape. Figures 2(e-i) illustrate this complete evolution in detail.

Brittleness

Diamonds are one of the hardest materials known to mankind, yet they also possess a remarkable fragility. This is due to their carbon atoms being held together by chemical bonds which cannot withstand external forces that could break them.

Diamond atoms are organized in a tetrahedral lattice structure, meaning the carbon atoms cannot be moved much without bending or cracking. This makes diamond jewelry an incredibly hard and durable material.

The Hydraulic Press Channel, a YouTube channel that specializes in crushing objects with a hydraulic press, decided to test how hard it is to break diamonds. In this video, they smash an impressive 1.2 carat diamond into millions of pieces.